Electric discharge device



May 14, 1963 D, A. LARSON ETAL ELE CTRIC DISCHARGE DEVICE Filed July 14, 1960 FIG.

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United States Vania Filed July 14, 1960, Ser. No. 42,796 9 Claims. (Cl. 313-34) This invention relates to electric discharge devices and, more particularly, to a highly-loaded fluorescent lamp and means for controlling the mercury-vapor pressure thereof during operation.

As is well known, the efficiency and light output of a fluorescent lamp is dependent upon the mercury-vapor pressure within the lamp. It is also well known that optimum eficiency and light output occurs when the mercury-vapor pressure is maintained within the range of about 6 to microns and that this pressure can be obtained by providing a region within the lamp that has an operating temperature between about 40 to 45 C.

Conventional fluorescent lamps having a loading of around 10 watts per foot of lamp length present no difficulty in this regard since substantial portions of the bulb wall inherently operate in the aforesaid temperature range. However, in the so-called highly-loaded fluorescent lamps (that is, those which operate at loadings of 25 watts per foot of lamp length and higher) more heat is generated within the gaseous discharge which, in turn, causes the envelope to operate at a much higher temperature. In order to avoid the resultant decrease in light output and efficiency it is accordingly necessary to provide a cool region or so-called cooling chamber within such highlyloaded lamps that will maintain the mercury-vapor pressure at the desired value.

Various means have heretofore been employed to provide such cooling chambers. Among these have been the use of a tubulation that projects radially outward from the center of the envelope, and the use of longer stem mounts at each end of the lamp which mounts are fitted with heat shields that separate the ends of the envelope from the cathodes to form end chambers. However, the aforesaid structures leave much to be desired insofar as the radially extending tubulation is susceptible to breakage, produces strains in the glass and detracts from the appearance of the lamp; whereas the elongated cooling chambers at each end of the envelope shorten the arc length and produce dark ends. In addition, both of these designs require the use of additional parts and assembly operations which increase the manufacturing cost of the lamp.

With the foregoing in mind it is the general object of this invention to provide an improved metallic-vapor discharge device that will operate at a preselected vapor pressure and can be easily and inexpensively fabricated.

Another and more specific object is the provision of a highly-loaded fluorescent lamp that will operate at optimum efliciency and is of rugged and simple construction.

Still another object of this invention is the provision of an improved vapor pressure control means and accommodating base member for a highly-loaded fluorescent lamp wherein certain parts serve a dual purpose and the total number of parts required are accordingly kept to a minimum.

The foregoing objects, and others which will become apparent to those skilled in the art, are achieved in accordance with this invention by utilizing as the cooling means the axially-extending exhaust tube that is normally provided on one of the electrode mount assemblies sealed to the ends of the bulb. The exhaust tube is merely tippedofl? at a point such that it is considerably longer than heretofore and is thus adapted, by virtue of its increased Patented May 14, 1963 length, to provide the desired region of decreased temperature within the lamp. The base attached to the end of the lamp having the aforesaid cooling tube is proportionately elongated and used to protectively enclose the tube in addition to its usual function of connecting the lamp to its socket.

In addition, the base is preferably constructed to insulate the cooling tube from the heat radiating from the adjacent end of the envelope and to maintain a flow of air past the tube so as to lower its operating temperature as much as possible and thus keep the length of both the tube and base to a minimum.

A better understanding of the invention will be obtained by referring to the accompanying drawing wherein:

FIG. 1 is an elevational view of a highly-loaded fluorescent lamp which incorporates the improved vapor pressure control means and base of this invention, the central part of the lamp being omitted for convenience of illustration;

FIG. 2 is an enlarged fragmentary view of the lamp shown in FIG. 1, mainly in section, showing the cooling tube and base construction of this invention in greater detail;

FIG. 3 is a plan view of the end of the lamp shown in FIG. 2 that has the cooling tube and modified base in accordance with the invention;

FIG. 4 is a cross-sectional view through the basal end of the lamp along the line IV- IV of FIG. 2, in the direction of the arrows;

FIG. 5 is an exploded perspective view of the base mem: ber shown in the preceding figures; and

FIG. 6 is a cross-sectional view corresponding to FIG. 4 but showing another type of base according to the invention.

While the present invention maybe advantageously employed in various types of vapor discharge devices that require means for controlling the vapor pressure during operation, it is especially adapted for use in conjunction with highly-loaded fluorescent lamps and accordingly has been so illustrated and will be so described.

In FIG. 1 there is shown a highly-loaded fluorescent lamp 10 comprising a sealed tubular and radiation-transmitting envelope 12 having bases 13 and 14 attached to each of its ends. Each base is provided with a protruding elongated boss 15 and 16 of insulating material which bosses are appropriately contoured, as is well known, 'to accommodate recessed contacts for connecting the lamp to a socket and an electrical power source. As is shown more particularly in FIG. 2, reentrant type stems 19 and 20 are sealed to the ends of the envelope 12 and support the usual activated electrodes 21 and 22, respectively, in operative relationship Within the envelope. The inner surface of the envelope is coated with the customary UV- responsive phosphor 13 and the envelope is charged with a predetermined quantity of mercury 32 and a suitable starting gas such as neon or argon, or a mixture thereof, in the usual manner.

In accordance with this invention the axially-extending exhaust tribulation that is normally provided on one of the stem assemblies, the stem 20 as illustrated in FIG. 2, and which communicates with the interior of the envelope 12 through an aperture 33 in said stem, is used as the cooling chamber. This is accomplished by tipping-oif the aforesaid exhaust tubulation at a point much further fromthe end of the envelope than heretofore thereby to provide a cooling tube 30 of such length and diameter that at least a part thereof has a lower operating temperature than the envelope proper. More specifically, the length and diameter of the cooling tube 30 is such that itprovides a cool region within the lamp that has an operating temperature within the desired range of about 40 to ice 45 C. As a result, the mercury 32 will tend to con-' 3 dense within the cooling tube 30 (as shown in FIG. 2). thereby maintaining the mercury-vapor pressure within the prescribed limits for optimum efliciency and light output without the use of any additional tubulation or sealing operations.

As shown in FIG. 1, the base 13 is of the usual shallow construction whereas the base 14 is elongated so as to protectively enclose but remain spaced from the cooling tube 30. A heat barrier or shield 34 of suitable low heat-conductive material such as plastic is desirably provided inside the base to insulate the cooling tube 30 from the heat radiated from the adjacent end of the envelope 12.

As shown more particularly in FIGS. 2, 3 and 5, the base 14 consists of a cylindrically hollow shell, preferably of molded plastic, that is open at one end and partly closed at the other end by an end Wall 17 and the aforesaid boss 16, which boss has a central opening 26 and lead wire passages therethrough. Cavities 28 in the outer face of the boss 16 connect the central opening 26 with the aforesaid passages and provide recesses for either the lamp contacts or for the lead wires 23 and 24 that are sealed through the stem 20, depending upon the type of base and terminal construction employed. The outer ends of the lead wires may be flattened and bent into the aforesaid recess cavities and opening and thus used as the lamp terminals so as to provide the desired recessed contact structure at minimum cost. This type base and terminal construction is disclosed and claimed in copending application Serial No. 784,488, W. Pechy, filed January 2, 1959, and assigned to the assignee of the present invention.

A circumferential shoulder or abutment 36 (see FIGS. 2 and on the inner surface of the base shell proximate the open end thereof serves as a seat for the heat shield 34 and divides the shell into a lamp-receiving portion and an elongated intermediate portion along a plane transverse to the base axis. The heat shield 34 is of circular configuration and dimensioned and keyed so as to be registrably insertable into the base against the abutment 34. When thus disposed, it partitions the outwardly disposed portion of the base 14 from the envelope 21 and together with said portion forms a compartment or enclosure A for the cooling tube 30. The aforesaid tube and lead wires 23 and 24 axially project through an elongated opening 35 in the shield 34 and therebeyond into centrally located position within the enclosure A, with the leads passing through and into the boss 16 as shown.

Vent openings 18 are desirably provided in the intermediate portion of the base shell and are preferably disposed in the same plane as the lead wires 23 and 24, as shown in FIG. 4, and the recess cavities 28 so as to be located above and below the cooling tube tube 30 when the boss 16 is vertically disposed. In this manner a thermally induced current of air will flow past the cooling tube 30 when the lamp is operated with the boss 16 in such position. The vents also permit radiation from the warmer components in the enclosure A to escape.

If desired, groups of vent openings 18a and 38 circumferentially spaced approximately 90 from each other with one pair of diametrically opposed openings disposed in approximately the same plane as the lead wires and recess cavities may be provided, as shown in the alternative embodiment illustrated in FIG. 6, to permit the desired convection cooling to occur regardless of whether the lamp 10 is operated with the boss 16 disposed in a vertical or horizontal position.

In order that the desired regulation of the mercuryvapor pressure may be obtained with a cooling tube 30 and base 14 of the shortest possible length, the surface of the heat shield 34 facing the envelope 12 is preferably coated with a material 37 (see FIGS. 1 and 5), such as aluminum or the like, that is highly reflective to infrared radiation so that the heat energy emanating from the electrade will be reflected back into the lamp.

As will be understood, the exact diameter and length of the cooling tube 30 will vary considerably depending upon the wattage rating of the lamp, the type of metal vapor employed therein, etc. has been found that a highly-loaded 100 watt T12 fluorescent lamp approximately 4 foot in length and containing a fill gas of neon-20% argon at 2 mm. pressure and mercury, operated at its rated wattage and etficiency when provided with a cooling tube having an outside diameter of approximately a wall thickness of approximately 1 mm, and which extended 1" beyond the sealed lip of the envelope. Arc voltage measurements taken while the lamp operated at rated watts and efliciency showed that a vapor pressure equivalent to a temperature of about 43 C., or approximately in the middle of the permissible range, was maintained with this particular combination of lamp and tube.

By using a cooling tube as above described rather than cooling chambers at the ends of the lamp, lamps have been made which operate at the same wattage and have the same electrode spacing as end cooled lamps but which are 2 /2" shorter in overall length. If the arc length of the lamp having the cooling tube were increased by this same amount so as to provide a lamp having the same overall length, the wattage and light output thereof would be increased by approximately 6 /2 The aperture 33 is approximately the diameter of the cooling tube 30. If desired, two heat shields may be used in each base to provide an insulating air space and both ends of the lamp 10 may be provided with cooling tubes. This latter feature will decrease the time required for the mercury-vapor pressure to reach its equilibrium value.

It will be recognized from the foregoing that the objects of the invention have been achieved by providing an improved highly-loaded fluorescent lamp and vapor pressure control means therefor. By utilizing the exhaust tube as the cooling chamber and one of the base members as a protective enclosure for the elongated tube, a lamp structure is provided which is not only exceptionally rugged but which requires a minimum of parts and labor for its manufacture.

While several embodiments have been illustrated and described, it is to be understood that various modifications in the configuration and organization of parts may be made without departing from the spirit and scope of the invention.

We claim:

1. A metallic-vapor discharge device of the type designed to be operated under such conditions that the metallic-vapor pressure normally would be higher than that required for optimum efficiency, comprising a sealed envelope containing spaced electrodes between Which a gaseous discharge occurs during the operation of said device, a tubulation integral with and extending from one end of said envelope, and a base attached to said one end of said envelope protectively enclosing but spaced from said tubulation, said base having an envelope-receiving portion and an intermediate vented portion, the outer end of said tubulation being closed and the inner end thereof being open and communicating with the interior of said envelope, said tubulation extending a considerable distance beyond the end of said envelope and into the intermediate vented portion of said base, the length and diameter of said tubulation being such that at least a part thereof has a lower operating temperature than said envelope and thereby provides a cool region within said device that reduces the metallic-vapor pressure and maintains it at approximately the desired value.

2. A metallic-vapor discharge device as set forth in claim 1 wherein said base includes a transverse shield that insulates the closed end segment of said tubulation from the heat emanating from the adjoining end of said envelope.

3. A mercury-vapor discharge lamp of the type de- As a specific example, it p signed to be operated under such conditions that the mercury-vapor pressure normally would be higher than that required for optimum light output, comprising a sealed tubular radiation-transmitting envelope containing a pair of spaced electrodes at least one of which is supported by a stem sealed to one end of said envelope, a vitreous tube hermetically joined to said stem and extending axially outward therefrom, a vented base attached to said one end of said envelope protectively enclosing but spaced from said tube, and a heat shield of low heat-conductive material within said base located proximate the end of said envelope transversely of the lamp axis, said tube projecting through an opening in said heat shield and extending a substantial distance therebeyond, the outer end of said tube being sealed oh? and the inner end thereof communicating with the interior of said envelope through an aperture in said stem, said tube having a length and diameter such that at least a part thereof has a lower operating temperature than said envelope and thereby provides a cool region Within said lamp that reduces the mercury-vapor pressure and maintains it at approximately the desired value.

4. A mercury-vapor discharge lamp as set forth in claim 3 wherein said base has vent openings located above and below said tube when said lamp is oriented in the poition in which it normally is operated.

5. In combination with a highly-loaded fluorescent lamp that includes a sealed tubular radiation-transmitting envelope which contains a charge of mercury and has a stem at one end from which a pair of lead wires extend, a vitreous tube fused to said stem and communicating with the interior of said envelope through an aperture in said stern, a base attached to the said end of said envelope, and a heat shield in said base partitioning the outwardly disposed portion thereof from said envelope, said vitreous tube and lead wires projecting through an opening in said heat shield and into the enclosure formed by said heat shield and said outwardly disposed portion of said base, a plurality of openings in said base located to permit the circulation of air through said enclosure and past the portion of said vitreous tube disposed therewithin, the outer end of said vitreous tube being sealed off and said tube having a length and diameter such that at least a portion thereof has a lower operating temperature than said envelope, whereby said vitreous tube serves as a cooling chamber for and maintains the mercury-vapor pressure at approximately the value required for optimum light output.

6. The combination of a base, heat shield and vapor pressure regulating tube in a highly-loaded fluorescent lamp as set forth in claim 5 wherein, said stem is of the reentrant type, and said base is provided with recessed contacts for connecting said lamp with an electrical power supply.

7. A base for an electric discharge lamp comprising, a cylindrically hollow shell that is open at one end and partly closed at the other, a circumferential abutment on the inner surface of said shell located proximate the open end thereof and dividing said shell into a lamp-receiving portion and an elongated intermediate portion along a plane transverse to the axis, an apertured circular heat shield of low heat-conductive material insertable into the lamp-receiving portion of said shell against the aforesaid abutment, and a pair of opposed recess cavities in the end of said shell opposite the open end thereof for accommodating the terminals of said lamp, said intermediate portion of said shell having at least two vent openings therein located in approximately the same plane as said opposed recess cavities.

8. A lamp base as set forth in claim 7 wherein at least one side of said heat shield is coated with a material that reflects infrared radiation.

9. A lamp base as set forth in claim 7 wherein said intermediate portion of said shell has a plurality of vent openings therein circuniferentially spaced approximately from each other with one pair of diametrically opposed openings disposed in approximately the same plane as said recess cavities.

References Cited in the file of this patent UNITED STATES PATENTS 2,535,773 Yoder Dec. 26, 1950 2,957,995 Fox Oct. 25, 1960 FOREIGN PATENTS 784,859 Great Britain Oct. 16, 1957 936,527 Germany Dec. 15, 1955 

1. A METALLIC-VAPOR DISCHARGE DEVICE OF THE TYPE DESIGNED TO BE OPERATED UNDER SUCH CONDITIONS THAT THE METALLIC-VAPOR PRESSURE NORMALLY WOULD BE HIGHTER THAN THAT REQUIRED FOR OPTIMUM EFFECIENCY, COMPRISING A SEALED ENVELOPE CONTAINING SPACED ELECTRODES BETWEEN WHICH A GASEOUS DISCHARGE OCCURS DURING THE OPOERATION OF SAID DEVICE, A TUBULATION INTEGRAL WITH AND EXTENDING FROM ONE END OF SAID ENVELOPE, AND A BASE ATTACHED TO SAID ONE END OF SAID ENVELOPE PROTECTIVELY ENCLOSING BUT SPACED FROM SAID TUBULATION, SAID BASE HAVING AN ENVELOPE-RECEIVING PORTION AND AN INTERMEDIATE VENTED PORTION, THE OUTER END OF SAID TUBULATION BEING CLOSED AND INNER END THEREOF BEING OPEN AND COMMUNICATING WITH THE INTERIOR OF SAID ENVELOPE, SAID TUBULATION EXTENDING A CONSIDERABLE DISTANCE BEYOND THE END OF SAID ENVELOPE AND INTO THE INTERMEDIATE VENTED PORTION OF SAID BASE, THE LENGTH AND DIAMETER OF SAID TUBULATION BEING SUCH THAT AT LEAST A PART THEREOF HAS A LOWER OPERATING TEMPERATURE THAN SAID ENVELOPE AND THEREBY PROVIDES A COOL REGION WITHIN SAID DEVICE THAT REDUCES THE METALLIC-VAPOR PRESSURE AND MAINTAINS IT AT APPROXIMATELY THE DESIRED VALUE. 